I think a simulation (Y) is a process of mimicking something else (X). In which case we should not observe in Y something (Z) that couldn't happen in X.

So maybe we should rather say that Y is a game with otherwise X-like rules, but additional rules that allow Z, rather than calling it simulation. Or at least I think if "simulation" Y is not an accurate simulation of X, we should use some explicit qualifier to indicate its non-accuracy.